四川地区强震发生条件的综合分析

根据发震断层的时代，发震构造的应力和几何结构条件，对四川地区的强震发生条件进行了综合分析，结果表明，四川地区孕育和发生强震的断层主要晚更新世以来，特别是全新世以来活动的断裂；强震多发生在主压力方向与断层交角成３０°～６０°之间的最危险滑动角值范围，走滑断层的斜列状结构，断裂的交叉结构，断裂的枢纽结构，断裂上的弯曲，转折部位以及断裂带上的横向隆起，拗陷及其交接部位都是发震构造的结构特征，有利于强震的     

邢台震区深部构造与强震孕育关系的探讨

将地壳介质视为马克斯威尔体,运用三维有限元方法,探讨分层地壳结构中存在高速体、低速体和深部断裂时,地壳应力的集中及应力集中随时间演化的特征．计算结果表明:① 由于地壳的非均匀性,在高速体内形成高平均应力集中条带,在高速体内和深部断裂附近形成水平最大剪应力（以下简称最大剪应力）高集中区．平均应力扰动值随时间的变化趋势,导致在漫长的地质年代内,平均应力在地壳内有趋向一致的变化趋势．最大剪应力扰动值随时间的变化,导致低速体内的剪切应变能向高速体内转移;② 当地幔以1 cm/a速率上隆时,平均应力扰动值随时间的变化比较复杂,高速体和低速体的边界已不是那么明显．在高速体内沿狓方向的两个边区,最大剪应力扰动值随时间更加高速地增长,这种应力演化更有利于实现低速体内的剪切应变能向高速体内转移;③ 在深部断裂带的下半段附近,平均应力和最大剪应力扰动值随时间的变化趋势,导致在较长时间内积累较高的剪应力,最后引起深部断裂失稳和沿断层方向的加速蠕滑;④ 深部断裂沿断层方向的加速蠕滑,可以使深部断层两侧地表面垂直位移的变化,与邢台地震震前一年的地表面垂直位移变化趋势非常一致．深部断裂的加速蠕滑可能是震前地表垂直位移异常变化的原因之一．      

山西地震构造带强震发生的地震地质条件

山西地震构造带内与强震活动有关的断裂多为北北东—北东走向的高角度正断层,是位于重力梯度带上的深断裂、新生代以来长期活动、新构造运动强烈活动的下沉地段、是许多强震的发震区.山西地震构造带下部上地幔是个隆起带,许多强震发生在上地馒隆起的斜坡带上,那里是地壳厚度变异带,分布有切割莫氏面的深断裂.地壳上层构造与深部构造相互结合、互相制约是山西许多强震发霉必要的地质构造条件.水平与垂直相互叠加的应力场是强震发震的应力条件,而且垂直挤压应力起重要的作用.     

邢台地震区地壳速度结构特征与强震孕育发生的关系

运用三维有限单元法,探索地壳结构的非均匀性对地壳应力场的影响．假定分层地壳结构中镶嵌高速块体,低速块体,高、低速块体３种情况,分别计算壳内平均应力与水平剪应力的变化图像．结果表明：高速块体单独存在可导致高应力在高速体内的局部集中,并在其边缘和四个角区形成应力的高度集中,有利于强震的孕育和发生;低速体单独存在时,由于低速体本身不能积累应力,而其上部的应力集中程度不大,难以形成强震;高、低速体的同时存在则有利于高应力在高速体内的高度集中和在高速体外的地壳上、下部的相对集中,形成对大地震孕育、发生更加有利的条件．本文结果与邢台地震序列的空间分布图像吻合甚好．     

唐山地震深浅构造关系研究

地表观察和浅层高分辨率地震探测表明 ,唐山断裂与地震地表主破裂带的位置、产状均一致 ,且具有高角度西倾的逆冲走滑性质 ,发生过右旋水平错动和向东逆冲的垂直活动 ,而次破裂带与褶皱构造活动引起的其他断裂直接相关。根据瞬变磁场和深地震探测结果分析 ,唐山地区存在莫霍面斜坡和地壳“背斜”、中地壳水平滑脱和扩展断裂、上地壳高角度逆冲走滑断裂和背向斜构造 ,它们组成 1幅多层次、多级序的复式逆断裂 -扩展背斜构造图像 ,控制了唐山地震的孕育和发生     

四川地区强震与发震构造几何结构特征关系的探讨

本文通过近些年来对四川活动断裂与强震关系的研究，初步总结了四川地区强震与发震构造几何结构特征的关系。作者认为：走滑断层的斜列状结构，断层的交叉，大断裂带的末端，断裂上的枢纽、弯曲、转折部位以及断裂带上的横向隆起、拗主其交替部位都可能是发震构造的结构特征，亦是强震易于发生的部位，这对地震危险区域潜在震源区的划分及其地基预报、地震区划和工程区地震安全性评价具有重要的意义。     

南汀河西支断裂深浅构造特征——来自深地震反射剖面的证据

云南省西南部,发育一组由不同断裂组成的北东向断裂构造带,沿这些断裂数十年来相继发生过多次强震.本文以其中的南汀河西支断裂为研究对象,采用深地震反射剖面方法,获得了断裂及两侧地壳精细结构和构造图像.探测结果表明:研究区纵向上,分为上、下两层地壳结构,总厚度约为31.25~35.6 km;横向上,以南汀河西支断裂为界,两侧反射特征差异较大,分别以弧状或倾斜反射波组为主·测线经过地区,莫霍面反射特征较为清晰,为2-3个反射同相轴组成的反射条带.南汀河西支断裂为一个由5条分支断层组成的断裂带,呈花状结构,反映了一种走滑挤压的应力状态.断裂带下方,存在一条切穿下地壳及莫霍面并延伸至上地幔的深大断裂·这种深、浅断裂共存的构造格局是控制南汀河地区地震孕育和发生的重要因素之一.     

1966年邢台地震群的发震构造模型——新生断层形成?先存活断层摩擦粘滑?

通过对邢台地震极震区浅层探测、新生代深浅构造运动的分期、地壳上地幔结构特征剖析及其与震源参数的对比等研究,指出邢台地震区控制早第三纪盆岭构造发育的铲形断裂及其下部向东缓倾的滑脱面与邢台地震的发生无关;邢台地震群是在最新构造应力场作用下,受北西向断层或横向障碍体阻隔的不连续“深断裂”依次向上撕裂状破裂扩展、引起相邻斜列状深断裂间应力迁移和加载等三维破裂过程的产物;邢台地震断层是先存地壳“深断裂”向上撕裂状扩展的“新生断层”。     

邢台地震前地壳形变异常的可能性物理机制

将地壳介质视为麦克斯威尔体 ,运用差分法和三维有限元方法 ,探讨了邢台分层地壳结构模型 （含高速体和低速体及深大断裂 ）中深部断裂加速蠕滑时 ,平均应力、水平最大剪应力和地表面垂直位移随时间演化的特征 ,计算结果表明 :（1 ）在地壳中上部 1 1km处 ,深部断裂的加速蠕滑急剧加速了水平最大剪应力的增加速率 ,可达数百倍 ,深部断裂的加速蠕滑是邢台强地震成核过程的开始 ,可实现地壳下部的能量向地壳中上部快速转移 ;（2 ）深部断裂的加速蠕滑引起的地面垂直位移变化与邢台地震震前的地表面垂直位移变化非常一致 .说明邢台地震震前地壳表面垂直方向的位移不仅与岩石的膨胀有关 ,而且可能与地壳内深部断裂的加速蠕滑密切相关 .     

中国甘肃昌马断裂带及其现代活动

昌马断裂带是是青藏高原北部一条活动强烈的左旋走滑断裂带。它表现为重力、航磁、地壳厚度的综合异常梯度带，属于断面陡、切割深的超岩石圈断裂。昌马断裂带由１２条长４公里至１８公里不等的不连续的主断层和４条次级断层组成，可划分为东、中、西三大段落。断裂的水平位移和滑动速率具有分段性，全新世以来，东、中、西三段的左旋水平滑动速率分别为４．１毫米／年，２．６毫米／年和１．５毫米／年。北东东、北北西和北西西三个方向断层的位移具有分级特征，不同级别的位移具有良好的同步性。全新世以来北东东、北北西和北西西三个方向断层的水平滑动速率分别为４．１毫米／年、３．８毫米／年和２．７毫米／年。白垩纪以来，昌马断裂呈天平式运动，显示了枢纽断裂运动特征，枢纽轴位于断裂中段。昌马地震震源破裂性质及其反映的震源应力场与地震破裂带的破裂性质及其反映的构造应力场不一致。昌马地震震源机制解反映了北北西～南南东挤压，作用应力近于水平的震源应力场；昌马地震破裂带的变形组合反映了东北～南西挤压的构造应力场。昌马地震破裂带长１２０公里，分为东部正走滑段、中部逆走滑段和西部尾端破裂段，显示了多个水平位移峰值。全新世以来，沿昌马断裂发生了６次强震事件，强震复发     

THREE-DIMENSIONAL DEFORMATION CHARACTERISTICS OF THE XIANSHUIHE FAULT ZONE

In order to analyze 3-dimensional movement and deformation characteristics and seismic risk of the Xianshuihe fault zone, we inverted for dynamic fault locking and slip deficit rate of the fault using the GPS horizontal velocity field of 1999-2007 and 2013-2017 in Sichuan-Yunnan region, and calculated annual vertical change rate to analyze the vertical deformation characteristics of the fault using the cross-fault leveling data during 1980-2017 locating on the Xianshuihe fault. The GPS inversion results indicate that in 1999-2007, the southeastern segment of the fault is tightly locked, the middle segment is less locked, and the northwestern segment is basically in creeping state. In 2013-2017, the southeastern segment of the fault is obviously weekly locked, in which only a patch between Daofu-Bamei is locked, and the northwestern segment is still mostly in creeping state, in which only a patch at southeastern Luhuo is slightly locked from surface to 10km depth. The cross-fault leveling data show that annual vertical change rate of the Zhuwo, Gelou, Xuxu and Goupu sites on the northwestern segment is larger, which means vertical movement is relatively active, and annual vertical change rate of the Longdengba, Laoqianning, and Zheduotang sites on the southeastern segment is small, which means the fault is locked, and the vertical movement changes little before and after the Wenchuan earthquake. Combining with the 3-dimensional movement and deformation, seismic activity and Coulomb stress on the Xianshuihe Fault, we consider the seismic risk of the southeastern segment is larger, and the Wenchuan earthquake reduced the far-field sinistral movement and the fault slip deficit rate, which may reduce the stress and strain accumulation rate and relieve the seismic risk of the southeastern segment.     

THE SEISMOGENIC ENVIRONMENT ANALYSIS OF LUDIAN MS6.5 EARTHQUAKE USING GRAVITY DATA

The main rupture of Ludian M_S6.5 earthquake is directed to the northwest, which occurred in the east of Xianshuihe-Xiaojiang fault zone. The epicenter is in the transitional zone of the Sichuan-Yunnan block and the South China block, where there are many slip and nappe structures. Some controversy still remains on the earthquake tectonic environment. So, Bouguer gravity anomalies calculated by EGM2008 were broken down into 1-5 ranks using the way of Discrete Wavelet Transform(DWT), then we get the lateral heterogeneity in different depths of the crust. The distribution characteristics of Bouguer gravity anomaly are analyzed using measured gravity profile data. We also get its normalized full gradient(NFG)picture, and study the differences between different depths in crust. The results show that: (1)the characteristic of Buoguer gravity anomaly in southwest to northeast is high-low-high between the Lianfeng Fault(LFF)and Zhaotong-Ludian Fault(ZLF). The mainshock and aftershocks are distributed in the middle of the low-value zone, which means that the east moving materials of Qinghai-Tibet plateau broke through the southern section of Lianfeng Fault(LFF), moving along the Baogunao-Xiaohe zone(low-value belt)to the southeast, stopped by the Zhaotong-Ludian Fault(ZLF), and then earthquake occurred.(2)The third-order discrete wavelet transform(DWT)details show that: there is a good consistency between the negative gravity anomaly in upper crust and the distribution of major faults, which reflects that the rupture caused by the movements of the faults in crust has reduced gravity anomaly. There is a NW-trending negative anomaly belt near the epicenter, which may has some relationship to the southward development of the Daliangshan Fault(DLSF). So we speculate that the southward movement of Daliangshan Fault is the main direct force source of Ludian earthquake.(3)In the picture of the fourth-order DWT details, there is an obvious positive gravity anomaly under the epicenter of Ludian earthquake, which confirms the presence of a high-density body in the middle crust. While the fifth-order DWT details show that: A positive anomaly belt is below the epicenter too, which may be caused by mantle material intruding to the lower crust. Tensile force in crust caused by mantle uplift and extrusion-torsion force caused by Indian plate push are the main force source in the tensile and strike slip movement of the Ludian earthquake.(4)The normalized total gradient of Bouguer gravity anomalies of Huili-Ludian-Zhaotong profile shows that: there is obvious ‘deformation’ in the Xiaojiang fault zone which dips to the east and controls the local crust movement. There is a local ‘constant body’ at the bottom of the epicenter. The stable constant body in density has limiting effects to the earthquake rupture, which is the reason that the earthquake rupture' scale in strike and in depth are limited.(5)The ability of earthquake preparation in Zhaotong-Ludian Fault is lower than the Xianshuihe-Xiaojiang fault zone, and the maximum earthquake capacity in this area should be around magnitude 7.     

用滑动方向拟合法反演富蕴地震断裂带应力场

本文根据野外考察测得的1931年新疆富蕴8级地震形成的地震断裂带内42组断层水平和垂直位移数据,求得42个断层面上的滑动方向.利用滑动方向拟合法(使计算的断层面上的剪切力方向与观测的滑动方向之间夹角最小)求出了断裂带上由北向南四个区段的驱动断层滑动的平均应力场.结果表明,四个区段的最大和最小主压应力轴皆水平,最大主压应力轴方位大致在 N15E 至 N30E 之间.整个断裂带的应力场相当均一,这说明富蕴大地震的发震原因不象是局部因素,而可能是大范围构造运动的结果.      

中甸-大具断裂南东段晚第四纪活动的地质地貌证据

中甸-大具断裂南东段位于哈巴和玉龙雪山北麓,属于川西北次级块体西南边界,断裂总体走向310°~320°,是一条重要的边界断裂。了解该断裂的活动性质、活动时代和滑动速率等对分析川西北次级块体运动,研究该断裂与玉龙雪山东麓断裂的交切关系等问题具有重要意义。文中基于1︰5万活动断层地质填图,对断裂沿线地层地貌、陡坎地貌、地表破裂、典型断层剖面以及河流阶地等进行了详细的研究。研究表明:1)中甸-大具断裂南东段按几何结构、断错地貌表现、断裂活动性可分为马家村—大具次级段和大具—大东次级段。2)通过野外地质调查发现,马家村—大具次级段断错了全新世冲洪积扇,形成了地表破裂,为全新世活动段;而大具—大东次级段虽然也断错了晚更新—全新世地层,但其断错规模及滑动速率均较小,由此认为其全新世以来活动较弱。3)通过分析断裂沿线断层陡坎、水平位错及地表破裂等地质地貌问题,认为马家村—大具次级段的活动性质为右旋走滑兼正断,其晚更新世以来的垂直滑动速率为0.4~0.8mm/a,水平滑动速率为1.5~2.4mm/a;大具—大东次级段以右旋走滑为主、正断为辅,其晚更新世晚期以来的垂直滑动速率为0.1mm/a。4)在大具盆地内发现的NW向地表破裂带的形成时代很年轻,不排除是1966年中甸6.4级地震或1996年丽江7.0级地震造成的地表破裂。     

丽江7.0级地震震源环境及其破裂过程讨论

本通过对丽江Ｍｓ７．０地震发生环境和破裂过程的分析讨论，得到以下认识：丽江地震发生在滇西北裂陷区北部块体内，这是一个由三组深断裂切割包围的三角形断块，断块内发育有裂陷盆地（大具－丽江裂陷盆地）；该区除了水平应力作用外，还有很强的来自地幔物质上隆引起的垂直应力作用；主余震分布在地壳一个由相对低速区包围的高速区内。地壳介质结构横向非均匀性－地壳高速块体的存在，可能是丽江地震震源成核的重要成因。丽江７     

1999年台湾集集大地震的地表断层破裂特征

野外考察结果表明 ,1999年 9月 2 1日台湾集集大地震是由车笼埔断层发生逆冲作用造成的。地震产生的地表破裂长约 80km ,具有明显的挤压逆断层特征 ,其活动方式为具左旋性质的逆倾滑动。实测逆冲断层以 30°～ 50°的角向西北逆冲而上。断层的垂直位移量 ,南段约 2～ 3m ,北段约 3～ 8m ;断层的水平位移量 ,南段 0～ 3m ,北段 3～ 5m ;垂直断层的水平缩短量 ,南段 2～ 3m ,北段 3～ 6m。从台湾西部麓山带的地质构造剖面分析 ,地震震源恰好位于台湾西部麓山带中生代基底与其上的沉积盖层的界面的深度 ,而西部麓山带第三纪地层和其下的基底的分离面为一滑动面 (decolle ment)。在菲律宾海板块的挤压作用下 ,沿该区中生代基底之上滑动面的错动导致了地震的发生     

从地震折射和反射剖面结果讨论唐山地震成因

通过唐山震中的地震测深以及深反射剖面,揭示了唐山震源区的浅部及深部构造图象,它与以往的推测很不相同。 唐山东面的开平向斜属中生代构造,探测的结果表明,向斜轴是一近于直立的地壳断裂。唐山地震时的水平地形变主要是由开平地壳断裂的位移引起的,它是北北东-南南西向右旋走滑断裂。开平地壳断裂西面的陡河断层是一自地表向南东方向下插的正断层,断层倾角为26°,延伸至5km深处。陡河正断层刚好插到唐山市震中区的正下方。唐山地震时的垂直地形变主要是由陡河正断层的滑动引起的。 野鸡坨-丰台断层通过震源区的西部边缘,断层以西的第四纪沉积层,在过去一百万年间曾经沿北北东方向水平滑移15km,表明它也是一个右旋的走滑断层。但是它在近代数百年间并无地震活动,唐山地震时该断层的滑动亦不明显。 开平地壳断裂和陡河正断层在唐山地震时同时滑动,说明地震的作用力除区域水平构造力外,地壳上方还存在一个附加的引张力。在开平断裂处,上部地壳的反射面倾角杂乱,而且在它的正下方,莫霍界面明显错断,因此,地幔顶部的热物质可能自开平地壳断裂中上升。热物质产生的热应力在地壳上方可表现为张应力,而在地壳下方却表现为压应力,这与反射地震剖面图的现象相符合。开平地壳断裂中热物质的上升对地震的产生有     

A mechanical model for deformation and earthquakes on strike-slip faults

A two-dimensional model for stress accumulation and earthquake instability associated with strike-slip faults is considered. The model consists of an elastic lithosphere overlying a viscous asthenosphere, and a fault of finite width with an upper brittle zone having an elastoplastic response and a lower ductile zone having an elastoviscoplastic response. For the brittle, or seismic, zone the behavior of the fault material is assumed to be governed by a relation which involves strain hardening followed by a softening regime, with strength increasing with depth. For the fault material in the ductile, or aseismic, section, the viscous effect is included through use of a nonlinear creep law, and the strength is assumed to decrease with depth. Hence, because of the lesser strength and the viscous effect, continuous flow occurs at great depths, causing stress accumulation at the upper portion of the fault and leading to failure at the bottom of the brittle zone. The failure is initially due to localized strain softening but, with further flow, the material above the softened zone reaches its maximum strength and begins to soften. This process accelerates and may result in an unstable upward rupture propagation.Relations are developed for the history of deformation within the lithosphere, specifically for the velocity of particles within the fault and at the ground surface. The boundary-element method is used for a quantitative study, and numerical results are obtained and compared with the recorded surface deformation of the San Andreas fault. The effects of geometry and material properties on instability, on the history of the surface deformation, and on the earthquake recurrence time are studied. The results are presented in terms of variations of ground-surface shear strain and shear strain rate, and velocity of points within the fault at various times during the earthquake cycle.It is found that the location of rupture initiation, the possibility of a sudden rupture as opposed to stable creep, and also the ground deformation pattern and its history, all critically depend on the mechanical response of the material within the fault zone, especially that of the brittle section. Shorter earthquake recurrence times are obtained for shallower brittle zones and for a stiffer lithosphere. Lower viscosities of the aseismic zone and the absence of asthenospheric coupling tend to suppress instability and promote stable creep. The model results thus suggest that the overall viscosity of the ductile creeping zone must exceed a minimum value for a sudden upward propagating rupture to take place within the seismic section.     

Research on the seismotectonics of the Jan－uary 17，1995 Hanshin M7．2 earthquake

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